With the studies described in this proposal we would hope to continue our investigations into the role of vitamin E on platelet function. One of the most significant findings in our previous studies was the strong indication that Alpha-tocopherol may inhibit platelet adhesion. For this reason and the great significance such an action of vitamin E could have in Clinical Medicine we propose to examine the effect of vitamin E on platelet adhesion in greater detail both with respect to its demonstration in dynamic systems involving flowing blood, its possible mechanism of action, and the role played by endothelial cells beyond their production of prostacyclin. The effect of bioflavonoids, compounds structurally related to tocopherols and sharing anti-aggregating activity with them, will be determined under identical experimental conditions. Finally, some of the characteristics of endothelial cells obtained from vitamin E-deficient rabbits will be examined. Aspects of their interuction with platelets will be the principal targets of our study. We propose tht cyclic AMp metabolism, and membrane dynamics, both the fluidity of the lipid matrix and the motional freedom of membrane proteins are changed by Alpha-tocopherol to make platelets less adhesive. Experiments are planned with human and rabbit platelets in order to study the full range of Alpha-tocopherol levels from severe deficiency to marked enrichment. Dietary supplementation with vitamin E will be done both in humans and rabbits to obtain platelets of different vitamin E content. Deficiency of vitamin E will only be induced in rabbits. Adhesion will be measured in 3 systems utilizing flowing blood or PRP: 1) adhesion to subendothelium of rabbit aortas denuded of their endothelium by balloon catheter, 2) to glass surfaces coated with different extracellular matrix proteins and 3) to aspirin-inhibited endothelial cells of umbilical cords or rabbit aorta grown in culture and implanted into a flow cell. To identify the mechanism of the antiadhesive action of Alpha-tocopherol, measurements of fluorescence polarization of fluorescent lipophilic and protein ligand probes will be made as a function of the Alpha-tocopherol content of platelets and endothelial cells. Similar studies will be carried out with bioflavonoids. We expect that these studies will put the inhibitory effect of Alpha-tocopherol on platelet adhesion on a firm basis which can then lead to its rational use in thromboembolic diseases.